Illumination device

Abstract

Proposed is an illumination device (100), comprising a light source (110) such as an LED or a laser diode, a wavelength conversion medium (120) such as a phosphor, and a periodic antenna array (300) made of a highly polarisable material such as a metal. The light source emits primary wavelength light that at least partially is converted in secondary wavelength light by the wavelength conversion medium. The periodic antenna array is positioned in close proximity to the wavelength conversion medium and functions to enhance the efficiency of the absorption and/or emission processes in the wavelength conversion medium through the coupling of the incident primary wavelength light or the emitted secondary light to surface lattice resonances that arise from the diffractive coupling of localized surface plasmon polaritons in the individual antennas of the array. This is especially advantageous for forming low étendue illumination device suitable for use in projection systems, or for controlling the directionality, the polarization, and/or the color of the secondary wavelength light.

Description

FIELD OF THE INVENTION[0001]The invention relates to an illumination device. In particular it relates to such a device applying a wavelength conversion medium. Such a device is used in, for example, illumination systems, projection systems, and laser systems.BACKGROUND OF THE INVENTION[0002]An embodiment of an illumination device of the kind set forth is known from U.S. Pat. No. 7,709,811. That document discloses an illumination device comprising a blue LED (e.g. GaN or InGaN) light source, an internal optical element, a wavelength converting material, and an external optical element (e.g. a plastic or glass lens). The wavelength converting material (e.g. an organic dye or inorganic phosphor) is applied to a side of the internal element facing away from the LED. The internal optical element is a rectangular or pyramid shaped prism and serves to direct primary light emitted by the LED to the wavelength converting material. Moreover, it serves to redirect secondary light emitted by th...

AI Technical Summary

Benefits of technology

[0013]An embodiment of the invention according to claim 2 provides the advantage of improving the wavelength conversion process through the coupling of the incident primary wavelength light or the emitted secondary light to the surface lattice resonances that arise from the diffractive coupling of localized surface plasmon polaritons in the individual antennas of the array.

[0014]According to an embodiment of the invention, the periodicity of the antenna array is of the order of the primary or secondary wavelength light. Beneficially, this allows the light to excite surface lattice resonances.

[0015]The embodiment of the illumination device according to claim 4 beneficially allows controlling the modification of the illumination distribution of the device. This modification of the emitted light distribution from Lambertian to a more confined solid angle is especially interesting for low etendue lighting applications such as projection in beamers and automotive front lighting.

[0016]The embodiment of the invention of claim 5 advantageously allows for a better coupling of the primary and / or secondary wavelength light with the antennas and surface lattice resonances of the array.

[0017]In an embodiment according to claim 6, the stretchably controllable substrate allows active control of the emission efficiency, the directionality of the emission, and the emitted wavelength of the illumination device.

[0018]In embodiments according to claims 7 to 10, the two sub-arrays allow for appropriately designing the antenna array to accommodate several optical phenomena, such as, for instance, one sub-array enhances the excitation of the wavelength conversion medium, while the other sub-array enhances the emission of and defines the direction of the secondary wavelength light.

Problems solved by technology

Devices as disclosed by U.S. Pat. No. 7,709,811 exhibit several difficulties limiting their usefulness, such as heat management issues, efficiency issues, and emission directionality issues.

When concentrating light with such power levels in a relative small volume of phosphor material, the Stokes losses inherent to the wavelength conversion process result in high local heat dissipation.

This results in alleviated temperature levels of the phosphor which can easily exceed 200-300° C. At such levels, the conversion efficiency of the phosphors drops significantly, potentially resulting in additional power losses and uncontrolled further heating.

Such relatively large thicknesses may lead to an extended size of the light emitting area, especially when used in combination with laser light sources, and thus to a limited use of such devices as low éndue light sources in f.i. projection applications as beamers or car head lights.

While beam shaping optical elements are known to be useful to realize the application specific illumination distribution, these optical elements are usually bulky, need precise alignment with the LED and / or wavelength converting material, and are typically based on weakly dispersing materials (e.g. glass, plastics) which do not allow different beam shaping and beam directing of different light colors.

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